Method for plugging a well with a resin

ABSTRACT

A method for carrying out well construction, repair and abandonment operations, the method involves introducing a resin into a well and curing the same to form a seal, plug or connection, wherein the cured resin is expanded to at least the volume occupied by the resin prior to curing (compensating shrinkage), by cooling the well and curing the resin at a reduced temperature and subsequently allowing the well to reach its static bottom hole temperature. A method is also disclosed for analyzing the setting time, elastic properties, shrinkage/expansion, compressibility or coefficient of thermal expansion of thermosetting resins or oil well cements under simulated reservoir pressure and temperature conditions, which involves introducing a sample of a thermosetting resin or oil well cement into a pressure vessel that is equipped to provide the pressure and register the volume change to the analyzer used by this method.

FIELD OF THE INVENTION

This invention relates to a method for carrying out well construction,repair and abandonment operations with a thermosetting resin as seal,plug or connection. More in particular, this invention relates to amethod of improving the gas tightness of sealing materials in primarycementing, well repair and plugging operations in oil/gas wells.

This invention also relates to an analyzer for determining the settingtime, elastic properties, shrinkage/expansion, compressibility andcoefficient of thermal expansion of thermosetting resins and oil wellcements under simulated reservoir pressure and temperature conditions.

BACKGROUND OF THE INVENTION

The main objectives for drilling an oil or gas well are to create aconnection to an oil and/or gas reservoir and to install a conduit(called production tubing) between the reservoir and the surface. Theouter steel protection of a well is called the casing. The casingrequires a gas tight seal between the reservoir and the surface. Toachieve such seal, the annulus (the gap between the casing and therock/formation) is subjected to a cementing (or grouting) operation.This treatment is normally referred to as Primary Cementing. The mainaspects of primary cementing are to isolate flow between differentreservoirs, to withstand the external and internal pressures acting uponthe well by offering structural reinforcement and to prevent corrosionof the steel casing by chemically aggressive reservoir fluids.

A poor cementing job can result in migration of reservoir fluids, evenleading to gas migration through micro-annuli in the well which not onlyreduces the cost-effectiveness of the well but may cause a “blow out”resulting in considerable damage. Repair jobs (“secondary cementing”)are possible (in essence forcing more cement into the cracks andmicro-annuli). However, they are costly and do not always lead to thedesired results.

When a well has reached the end of its economical life, the well needsto be abandoned in compliance with local regulations. Abandonment isusually carried out by first plugging each of the casings in a largenumber of sequential steps, cutting and removing these cut steel casingstubs and successively placing large cement plugs in order topermanently seal the well. As only relatively small volumes of cement(typically in the order of 100 m) are used for those plugs, theirquality needs to be excellent as they will have to act as a seal for avery long time.

One of the major drawbacks of using traditional cementing materials suchas ‘OPC’ Class G Oil Well Cement (‘OPC’=Ordinary Portland Cement) inplugging operations is that this widely employed material cannot achievea gas tight seal due to its inherent shrinkage. The total chemicalcontraction can be split between a bulk or external volume shrinkage(less than 1%), and a matrix internal contraction representing 4-6% byvolume of the cement slurry, depending upon the cement composition(Parcevault, P. A. and Sault, P. H. ‘Cement Shrinkage and Elasticity: Anew Approach for good zonal Isolation’, paper SPE 13176 (1984). Thecombined shrinkage phenomena cause gas migration through micro-annuliand cracks. These are created because of those shrinkage phenomena andthe inherently poor adhesion of Oil Well cement to the steel Casing. Thealready poor adhesion is even further deteriorated by the inability toproperly clean the surface of the steel casing prior to cementing.

The use of conventional cementing materials in “remedial secondarycementing” has the disadvantage that the customary grain size is toolarge to pass freely into the micro-annuli and cracks which affect thequality of the seal.

In the search for effective cementing materials, attention has to bepaid to inter alia the following requirements: the material should begas-tight (i.e. withstand at least 2 bar per m), it should have acontrollable setting time so that a range of temperatures and welldepths (each requiring different conditions) can be coped with, itshould be thermally stable up to 250° C. as well as being chemicallystable against reservoir fluids for a very long period of time and itsrheological properties should be such that pumping through existing oilfield equipment can be carried out without too much problems.

A wide range of non cementious sealants have been suggested to cope withat least part of the problems outlined herein above. Examples of suchmaterials are resins (R. Ng and C. H. Phelps: “Phenolic/Epoxy Resins forwater/Gas Profile Modification and Casing Leak Repair” Paper ADSPE #90,presented at the ADIPEC, held in Abu Dhabi (16-19) October 1994);phenol-or melamine formaldehyde (W. V. C. de Landro and D. Attong: “CaseHistory: Water Shut-off using Plastic Resin in a High Rate Gravel packWell”—Paper SPE 36125 presented at the 4th Latin American and CaribbeanPetroleum Engineering Conference, held at Port of Spain in Trinidad,23-26 Apr. 1996); and polyacrylates (U.S. Pat. No. 5,484,020 assigned toShell Oil).

Although such materials can be instrumental in solving some of theproblems encountered with traditional, cement-based plugs, there arestill important drawbacks to be reckoned with in terms of handlingaspects, control of setting times and long term durability.

Also rubbers have been proposed in general for use as pluggingmaterials. Reference is made to U.S. Pat. No. 5,293,938 (assigned toHalliburton Company) directed to the use of compositions consistingessentially of a mixture of a slurry of a hydraulic cement (such asPortland cement) and a vulcanizable rubber latex. Rubbers specificallyreferred to in said U.S. patent specification are natural rubbers,cis-polyisoprene rubber, nitrile-rubber, ethylene-propylene rubber,styrene butadiene rubber, butyl rubber and neoprene rubber.

The vulcanization of the rubber involves the cross-linking of thepolymer chains which can be accomplished by incorporating one or morecross-linking agents (the most common one being sulphur) in the rubberlatex (latex having been defined as the aqueous dispersion or emulsionof the rubber concerned).

In European patent No. 325,541 (Merip Tools International S.A) the useof putty (“mastic”) has been disclosed for producing joints separatingzones in wells. Suitable compounds are formed by liquid elastomers suchas fluorosilicones, polysulphides, polythioethers as well as epoxy orphenolic resins. In addition, from International application WO 99/43923a special class of room temperature vulcanizing silicone andfluorsilicone rubbers is known that can be advantageously employed inthe repair and abandonment of wells.

Unfortunately, curing of non cementious plugging agents is alsoaccompanied by shrinkage, again potentially leading to micro-annuli andcracks in the sealant and/or lack of bonding of the seal, plug orconnection to its surroundings. This will especially occur if theadhesion of the thermosetting resin to the steel casing surface is lessthan the forces induced by the shrinkage process. It therefore remainsdesirable to further improve existing methods to overcome saiddrawbacks.

SUMMARY OF THE INVENTION

In accordance with the main embodiment of the invention there isprovided a method for carrying out well construction, repair andabandonment operations, which method involves introducing a resin into awell and curing the same to form a seal, plug or connection, wherein thecured resin is expanded to at least the volume occupied by the resinprior to curing (compensating shrinkage), by cooling the well and curingthe resin at a reduced temperature and subsequently allowing the well toreach its static bottom hole temperature.

The expression “resin” used in the main claim and throughout thespecification refers to “classic” thermosetting resins, as well asductile, vulcanizable rubbers.

Another embodiment of the invention comprises a method for removing aseal, plug or connection made of an expanded resin and used in wellconstruction, repair and abandonment, comprising the steps of a) coolingthe well, until the seal, plug or connection has shrunk loose, and b)removing the loose seal, plug or connection.

Finally, the invention also provides a method for analyzing the settingtime, elastic properties or shrinkage/expansion of resins or cementsused in well construction, repair and abandonment operations undersimulated reservoir pressure and temperature conditions, and theanalyzer used by that method.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a gas migration set-up; and

FIG. 2 is a schematic representation of a Rubber Augmentation Tester(LAB RAT).

DESCRIPTION OF THE INVENTION

In carrying out the process of the invention a well, preferably an oilor gas well, is cooled by a significant degree. The degree of cooling isdiscussed hereinafter. Next, a—preferably liquid—thermosetting resin orvulcanizable rubber is introduced and allowed to react (i.e. cure) untila solid, thermoset resin of nearly the dimensions of the surrounding“mold” is made. When the well is next allowed to reach its static bottomhole temperature, the seal, plug or connection will expand more than thewell due to the greater thermal expansion coefficients of resinscompared to the base materials of the well (e.g., carbon steel casing,primary cement having thermal expansions coefficients in the order ofrespectively 1.3*10−3 and 1.0*10−3 volume % per degree Centigrade (vol%/° C.), whereas that of resins may be e.g., 50-100× larger). Theexpansion should at least compensate for shrinkage, ensuring gastightness of the well, and better even expand beyond such dimension toensure a very firm bonding with the plug, seal or connector'senvironment.

Using a conventional resin, typically the well should be cooled by up toabout 100° C., for instance up to about 50° C., more suitably from about15 to about 40° C. For instance, the candidate well may be cooled bycirculation or (preferably) by injection of a cold fluid. This can beachieved via a workstring during a drilling/completion operation, or thecompletion tubing or coiled tubing for an already completed well.Suitable fluids can be (sea) water, completion brine, hydrocarbons ase.g. diesel, condensate or (to a lesser extent) a drilling fluid.

Other methods which could be envisaged is the ‘slurrying’ of ‘Dry Ice’(solid Carbon Dioxide) in the injection stream or cooling this stream atsurface with e.g. liquid Nitrogen in a fluid/fluid heat exchanger.

The degree of cooling depends on various parameters. For instance, apractical approach for a well engineer would be to estimate the degreeof cooling on the basis of well properties (e.g. static bottom holetemperature, length of the well bore, well geometry and presence ofaggressive chemicals), on the basis of the properties of the materialused in the well (steel, rock, cement), and on the basis of theproperties of the resin (e.g. amount of shrinkage upon curing,difference in thermal expansion coefficient vis-à-vis that of the wellmaterials; rate of curing at the lowered temperature), and on theavailability of a cooling medium. As to the latter parameter; it will beobviously easier for the well engineer to cool a High Pressure/HighTemperature (HPHT) well using ice cold sea water, than to cool a shallowwell in a continental Mediterranean zone, where only lukewarm water isavailable.

The above cooling temperatures are suggested for resins with no orordinary shrinkage upon setting and a thermal expansion coefficient 20to 200× that of the well material. Thus, cooling by more than about 100°C. will rarely by necessary, unless a resin with exceptionally largeshrinkage and/or exceptionally low thermal expansion coefficient isused.

Alternatively, and more precisely, the extent of cooling may be definedby the product of the temperature difference by which the well is cooled(ΔT in ° C.) and the difference in thermal expansion coefficient of theresin vis-à-vis that of the well material (ΔX in vol %/° C.). Forinstance, this product ΔT.ΔX is suitably in the range of from about 0.5to about 10, more suitably in the range of from about 2.0 to about 5,with the range of from about 3.0 to about 3.5 being preferred.

For even more accurate calculations as to the most suitable coolingtemperature, without endangering the integrity of the well by tooexcessive expansion, calculations by Finite Element Modeling (FEM), asdescribed by Bosma, Ravi et al may be used (SPE 56536, “Design Approachto Sealant Selection for the Life of the Well”, presented at the 1999SPE Annual Technical Conference and Exhibition, held in Houston, Tex.,Oct. 3-6, 1999). In fact, this article describes the desirability ofutilizing expanding ductile sealants, however, without any suggestion tocool the well first and use the thermal expansion of the thermoset resinto improve its bonding with e.g. the casing. Another model that may beused is described by Theircelin et al (SPE 38598, “Cement design basedon Cement Mechanical Response”, SPE Drilling & Completion, December1998, pp. 266-273).

To test the accuracy of the determination and/or provide physical dataon resin behaviour at well conditions, the present invention alsoprovides a specifically designed analyzer. This third embodiment of thepresent invention is described in more detail in the experimentalsection.

Thermosetting resins have been used in wells (oil, gas, water or evenwaste disposal wells) before. Those having a thermal expansioncoefficient significantly greater than 10−3 vol %/° C. may in principlebe used, as long as shrinkage occurring during curing is compensatedfor. Also mixtures of resins as well as mixtures with resins and othermaterials (e.g. Oil Well Cements, whether Ordinary Portland, BlastFurnace Slag or Aluminate) may be used.

For instance, U.S. Pat. No. 3,170,516 describes the recompletion ofwells, particularly oil and gas wells, wherein the bore of a well pipeis plugged with a liquid mixture of a thermosetting phenoliccondensation resin and a catalytic hardener thereof. Epoxy resincompositions that are curable to hard impermeable solids for use in wellbores have also been described in U.S. Pat. Nos. 3,960,801; 4,921,047;5,314,023; 5,547,027; 5,875,844; 5,875,845; 5,969,006; 6,006,834 and6,012,524, the contents of which are incorporated herein by reference;in International application WO 94/21886, and in European patentapplication No. 899,417. Most of these epoxy resins are base ondiglycidyl ethers of bisphenols, Bisphenol-A and Bisphenol-F inparticular, and such epoxy resins, if an epoxy resin is used, arepreferred.

Other thermosetting resins that have been used in well boreapplications, include ureum, phenol and melamine formaldehyde resins(Derwent abstracts 93-124473/15; 94-016587/03 and 89-032494/05); latexcompositions (U.S. Pat. Nos. 3,312,296; 4,537,918; 5,159,980; 5,738,463,the contents of which are incorporated herein by reference, and Derwentabstract 98-51909/44); the room temperature vulcanizing silicone andfluorsilicone compounds mentioned before; other resins such as disclosedin U.S. Pat. Nos. 4,898,242 and 5,712,314, the contents of which areincorporated herein by reference, and novel perfluoroether siliconehybrids (as disclosed in U.S. Pat. Nos. 5,310,846 and 5,342,879, thecontents of which are incorporated herein by reference) which aremarketed by Shin Etsu, Fremont, USA under the trade name SIFEL.

Suitable thermosetting resins may be selected on the basis of thethermal expansion coefficient of the resulting thermoset resin, and itsreaction (setting) rate. Thus, suitable thermosetting resins are thoseresulting in a thermoset resin preferably having a thermal expansioncoefficient that is greater than about 0.0015 vol %/° C., morepreferably is in the range of from about 0.02 to about 0.20 vol %/° C.(as measured by the apparatus disclosed as the third embodiment of thisapplication). Besides, the thermoset resin should set sufficientlyquickly to benefit from the thermal expansion coefficient when the welltemperature increases, e.g. it should react fully in the order of hourscompared with the tens of hours required to allow the well to regain itsinitial (bottom hole static) temperature. Furthermore, suitable resinsshould be impervious to gas, oil, brines and well-treating chemicals atwell operating temperatures and pressures.

Particularly suitable resins for use in the methods of the presentinvention are elastomeric thermoset resins. For instance, thevulcanizable rubbers of U.S. Pat. No. 5,293,938; European patentapplication No. 325,541 and/or international application WO 99/43923,all incorporated by reference, may be used.

With respect to the thermosetting resins mentioned before and in thesection on the background of the invention those of WO 99/43923 areparticularly preferred. These RTV silicone rubbers include thecondensation products of silanol terminated polymers with across-linking agent, as well as the addition/curing (fluor)siliconecompositions described therein.

Good results in accordance with the present invention can be obtainedwhen using a two component Room Temperature Vulcanizing (RTV) siliconerubber or fluor-containing RTV silicone rubber. Such two componentsystems comprise two base chemicals: a hydride functional silicone crosslinking agent and a vinyl functional silicone polymer. When these basecompounds are brought into contact they will react, presumably via theaddition-curing principle as discussed herein before, thereby producinga (fluor)silicone rubber or gel type material. One of the advantages ofthis curing system is that it does not require an external reagent toinitiate reaction (like water, e.g. present in moist air). A furtheradvantage of this curing system is that it does not produce unwanted ordamaging by products like alcohols or acetic acid. It is also notlimited by diffusion of one of the reactants (e.g. moist air) into theother very viscous component. Therefore, the reaction of the twocomponents will proceed independently of their respective volumes.

International application No. WO 99/43923 describes RTV (fluor)siliconerubbers for: (1) zonal isolation, a) as an alternative to primarycementing in conventional well completion applications, or b) incombination with Expandable Tubing (cf. PCT/EP00/03039); (2) as wellrepair method for corroded tubing, and (3) to fill External CasingPackers. It should be realized that the method of the present inventioncan be used in a similar fashion.

As such, the thermosetting agent is placed in the well, at a desireddepth and location (e.g. in the annulus during a primary cementation oras a plug, in a “plug and abandonment” operation). Prior to placement,the well will have been cooled by one of the methods described in thepreceding text.

Due to the (significantly) higher thermal expansion of the thermosetresin (e.g., the RTV (fluor)silicone rubbers described in WO 99/43923expand by some 0.06-0.08 vol %/° C.), the resin will expand more thanthe rest of the completion upon re-heating of the well, which 1) willmore than compensate for any shrinkage incurred during the setting ofthe resin (typically some 0.6% upon setting from the liquid to the solidphase) and 2) will improve the chemical and/or physical adhesion processof the resin to the casing wall.

The seal may be further improved by enclosing it between a cementpre-flush and after-flush. To enable the placement of such acement-resin-cement sandwich in a Plug and Abandonment (P & A)application, the cement pre-flush preferably has a higher density thanthe thermosetting resin which may be achieved by the addition ofconventional weighting agents such as barite, hematite, trimagnesiumtetroxide, and the like.

Similarly, the cement after-flush preferably has a lower density thanthe thermosetting resin, e.g. by the addition of extenders e.g.lightweight fillers, hollow microbeads and the like.

According to another embodiment, which is basically an extension of theembodiment described herein before, the invention also provides a methodfor removing a seal made of a thermoset, expanded resin, by cooling thewell wherein the seal is used until the seal has sufficiently shrunk toallow its (non-destructive) removal.

Whilst the above process has been described in combination with welltechnology applications, it should be realized that the invention is notso limited. Indeed, the process of the present invention may also beapplied in surface facilities (e.g. temporary or permanent plugging ofpipelines and/or risers during e.g. platform (de)commissioningactivities, and abandonment of pipelines and the like).

The specific formulations can for instance be tested in the large-scalegas migration rig which has been described by Bosma et al in “Cementing:How to achieve Zonal Isolation” as presented at the 1997 OffshoreMediterranean Conference, held in Ravenna, Italy). The equipmentcomprises in essence a 4 meter high, 17.8×12.7 cm (7×5 inch) steelannular casing lay-out plus a 50 cm high simulated permeable (3000 mD)reservoir. The equipment can be operated at pressures up to 6 barg and80° C. The breakthrough of gas in the evaluation of the dynamic gassealing ability of a candidate sealing agent (e.g. cement or anothermaterial) during setting is monitored by flow transducers and, inaddition, pressure and temperature transducers placed equidistantlyacross the height of the column. A typical experiment is performed byapplying and maintaining a well-defined overbalance between cementcolumn and “reservoir” pressure and monitoring the dependent parameters(flow, pressures and temperatures) versus time.

It is also possible to use a static type of test equipment, e.g. asdescribed in the paper SPE 1376 presented by P. A. Parceveaux and P. H.Sault at the 59th Annual Technical Conference and Exhibition in Houston,Texas (Sep. 16-19, 1984) entitled “Cement Shrinkage and Elasticity: ANew Approach for a Good Zonal Isolation”. The test equipment is inessence a high pressure static gas migration apparatus which can beoperated up to 200 barg and 150° C. and comprises a cylinder in whichappropriate internals such as plugs or annular casing configurations canbe simulated. Typically a cement (or other material) is allowed to setinside the cylinder at static conditions (i.e. no delta P). The sealantis either present as single phase of a resin, a hybrid (e.g. a mixtureof rubber latex compositions or RTV (fluor) silicone rubbers with OilWell Cements, either Ordinary Portland Cement, Blast Furnace Slag, orAluminate) or a sandwich of a thermoset rubber with a conventional OilWell Cement (either Ordinary Portland Cement, Blast Furnace Slag, orAluminate) on top of it (seen in the direction of the gas flow. Theresins are placed in this cell at a certain temperature (typicallyreflecting that of the cooled down well) and downhole pressure andallowed to set, whilst concurrently the cell is heated further to thefinal Bottom Hole Static Temperature (BHST) of the well (time frameapproximately one half to one day). Subsequently, the possible onset ofgas leakage is monitored by applying increasing pressure differentialsacross the plug or annular casing configuration, by decreasing the backpressure at the top of the plug. To calibrate the test equipment defaultcement formulations can be used.

The present invention also provides a method of analyzing the settingtime, elastic properties, shrinkage/expansion, compressibility orcoefficient of thermal expansion of thermosetting resins or oil wellcements under simulated reservoir pressure and temperature conditions,which comprises:

introducing a sample of a thermosetting resin or oil well cement into apressure vessel that is equipped with a means to provide the pressureand register the volume change, and that can accurately mimic realisticoil field conditions;

at least partly immersing a body in the sample;

filling the remaining volume of the vessel;

exciting the body by an external outside force; and

monitoring the progress of the setting reaction on a continuous basis bya frequency (vibration) measurement, which encompasses the determinationof the changing Resonance Frequency of the body that is at least partlyimmersed in the sample and which is excited by an external outsideforce.

The vessel may, for instance, be filled with a fluid that is eitherhydrophilic or hydrophobic, depending on the nature of the sample to beinvestigated.

The means to provide the pressure and to register the volume change maybe a pump or the like. For instance, excellent results have beenobtained using a syringe pump that is capable of maintaining constantpressure by moving a piston.

The body may be a flat spring, that is moving in the lateral direction.Alternatively, it may be a small cylinder, plate or the like moving inthe axial direction.

The body is preferably moved by an external magnetic field, but it mayalso be operated mechanically or similar fashion.

The present invention also provides an analyzer for determining thesetting time, elastic properties, shrinkage/expansion, compressibilityor coefficient of thermal expansion of thermosetting resins or oil wellcements by the methods described above.

Preferably, the analyzer is equipped with a flat spring that is excitedby an external magnetic field, a syringe pump, and a non magneticpressure vessel. The most preferred analyzer is described in theexperimental section.

The invention will now be illustrated by the following, non limitingExamples.

Test Equipment, the Large-Scale Migration Set-Up of FIG. 1

In FIG. 1 is shown a test set-up including a cylindrical pressure vessel1 provided with opposite end plates 2, 3, and an electrical heater 4 isarranged around the vessel 1.

A plug composed of a thermosetting resin part 6 and a cement part 8, isarranged in the pressure vessel 1. A filter layer 10 is arranged in thepressure vessel 1, between the first resin part 6 and the lower endplate 3. A temperature sensor T is arranged in the pressure vessel 1,between the cement part 8 and the end plate 2. A gas container Gc is influid communication with the interior of the pressure vessel 1 at thelower end thereof via a hydraulic line 10, and a back pressurecontroller Bpc is in fluid communication with the interior of thepressure vessel 1 at the upper end thereof via a hydraulic line 12.Hydraulic line 12 is provided with a flow indicator F, and pressuregauges P are provided at the respective hydraulic lines 10, 12. Acontrollable valve 14 is provided in a third hydraulic line 16interconnecting hydraulic lines 10, 12. The test set-up had a diameterof 14 cm and a length of 115 cm.

EXAMPLE 1

A series of experiments were conducted with the large-scale migrationset-up as described above. As thermosetting resin an RTV silicon rubber(based on DC 3-4230 from the Dow Corning Corporation, Midland, USA, andformulated to have a density of 2.33 g/cc, using silica flour andMicrofine Steel (100 Micron e.g. A-100 S ex Höganäs AB, Höganäs, Sweden)was selected, having a setting time of 6 hours at 100° C. A cement witha density of 1.92 g/cc and a setting time of 5 hours at 100° C. wasplaced on top of the resin. The simulated seal measured about 0.5 m ofresin and 0.5 m of cement.

The vessel 1 was closed and pressurized up to 200 barg by means of thegas pressure provided by the gas container GC. Whilst the resin andcement were setting, the set-up was heated within a time frame of half aday from 100° C. to 130° C., the simulated BHST of the well, to induceexpansion of the resin. Next, the pressure drop across the plug wasincreased in steps of about 10 bar up to 200 bar by successivelydecreasing the back pressure at the top of the plug by means of the backpressure controller BPC in order to determine the sealing capacity ofthe plug. The resin/cement sandwich appeared to be fully gas tight up to200 bar differential pressure, which was the limit of the test.

The experiment was repeated with the set-up in a slanted position,simulating a well with a 50° inclination vis-à-vis a vertical well.Again the seal withstood successfully the full 200 bar pressuredifferential.

COMPARATIVE EXAMPLE 1

The aforementioned experiments were repeated, however, with a curingtemperature of 130° C. instead of 100° C. and using a similar sandwichconsisting of RTV Silicone Rubber and Class G Oil Well cement. Thiscomparative experiment simulates the abandoning of an oil/gas wellwithout pre-cooling. The sealing capacity of the plug was only 30 bar,using a vertical set-up.

The experimental results show the gas tightness obtained whenpre-cooling a simulated oil/gas well by using a standard cement and anaddition-curing silicone formulation, in particular when applying suchformulations in sandwich type plugs.

Test Equipment, Analyzer at Down Hole T and P Conditions

To determine the setting behaviour, elastic/viscosity properties andvolume changes of the sealant materials (resin and cement) an analyzerwas developed as hereinafter described. A schematic representation ofthe analyzer is shown in FIG. 2.

This analyzer comprises a pressure vessel 20 to hold the sample 22, anda syringe pump 24 to provide the pressure and register the volumechange.

Pressure vessel 20 is a non magnetic (e.g. INCONEL) (INCONEL is atrademark) High Pressure, High Temperature Pressure vessel, which canaccurately mimic realistic oil field conditions.

The remaining volume of the vessel is occupied by a ‘pressurizationliquid’ that may be either hydrophilic or hydrophobic, depending on thenature of the reacting system to be investigated.

Pump 24 is capable of maintaining constant pressure by moving a piston26.

The progress of the setting reaction is monitored on a continuous basisby a frequency (vibration) measurement. It encompasses the determinationof the changing Resonance Frequency of a flat spring 28 which is excitedby an external Magnetic Field generated by a driving coil 30 (thefrequency being continuously swept over a frequency range of some 10-70Hz). The spring is partly immersed by the resin/cement system to betested and as such its resonance frequency will increase as the medium(in which it is immersed) will gradually ‘harden’.

The system can be either volume or pressure controlled, reflecting anisobaric or isochoric operational mode.

In a typical experiment, a continuous frequency sweep (ranging from 10Hz to 70 Hz) is applied by means of the driving coil 30 onto the flatspring 28 which is fixed at the vessel bottom at one end and which isfully free at the other end. A tiny permanent magnet 32 is mounted atthe spring 28 by a magnet holder 33 for excitation of the spring, dueits interaction with the continuously changing external magnetic fieldof the driving coil 30.

The input magnetic energy, which will result into an oscillation of thespring is fed into the pressure vessel by a highly magneticallyconductive pole shoe (not shown). The changing resonance frequencyresponse of the spring due to the change of the viscosity of thethermosetting resin or the oil well cement, is detected by a secondelectromagnetic coil 34 (externally mounted on a second pole shoe). Theoutput signal is then electronically conditioned prior to furtherprocessing.

The amplitude of the spring and its continuous change of resonancefrequency is fully automatically recorded by a Data Acquisition system(hosted by a portable PC).

The damping characteristics of the spring system (being related to theviscosity of the resin/cement and the ‘Spring Constant’ (being relatedto the elasticity of the liquid or solid) can be determined by aninternal algorithm.

As such not only a very clear monitoring of the onset of gelling/settingof oil well cements (and a multitude of resins and self vulcanizingrubbers) can be determined at in-situ well conditions, but also morefundamental data (elasticity modulus, viscosity), which can be used forwell engineering design.

The analyzer may also be used to determine the volume changes (atisobaric conditions) or alternatively the pressure changes (at isochoricconditions), whilst allowing the candidate cement or resin to set. Bothmeasurements can be performed at either isothermal conditions or forprescribed temperature sweeps over time.

In this manner, the volumetric properties (shrinkage or expansion) ofresins or oil well cements can be determined, or alternatively theircompressibility behaviour (in a time range from the onset of gelling upto far beyond ‘final set’ of the resin/cement) can be measured.

Also, the apparatus is capable to determine the volume change of thematerials under investigation as a function of temperature (i.e. thevolumetric thermal expansion coefficient, at isobaric conditions), bysweeping the temperature inside the vessel over a certain time period(max delta T of the prototype is about 270° C., i.e. −20° C. to +250°C.), whilst maintaining the applied pressure. (The maximum operatingpressure of the prototype is 1500 barg).

The latter (volume change) features can be de-coupled from the frequencyexciter set up (i.e. determination of the resonance-frequency),described earlier, and constructed as a separate apparatus.

EXAMPLE 2

The analyzer was used to measure the thermal expansion coefficient ofthe aforementioned RTV Silicone rubber, DC 3-4230 (ex Dow Corning,Midland, USA), being about 0.066 vol % per ° C. (at 200 barg), and tomeasure the volume change of the resin during setting (at 100° C., and200 barg), being about −0.5 vol %.

By comparison, a conventional Class G Oil Well Cement with a Water tocement ratio of 0.40, showed a total shrinkage of some 4-5% (at 100° C.,and 200 barg), after final setting and a thermal expansion coefficientof 0.001 vol % per ° C. (at 200 barg).

What is claimed is:
 1. A method for carrying out well construction,repair and abandonment operations, which method involves introducing aresin into a well and curing the same to form a seal, plug orconnection, wherein the cured resin is expanded to at least the volumeoccupied by the resin prior to curing, wherein the curing and expandingare done by cooling the well and curing the resin at a reducedtemperature and subsequently allowing the well to reach its staticbottom hole temperature.
 2. The method of claim 1, wherein the well iscooled by up to about 100° C.
 3. The method of claim 1, wherein theextent of cooling is defined by the product of the temperaturedifference by which the well is cooled (ΔT in ° C.) and the differencein thermal expansion coefficient of the resin vis-à-vis that of the wellmaterial (ΔX in vol %/° C.), and wherein this product ΔT.ΔX is in therange of from about 0.5 to about
 10. 4. The method of claim 1, whereinthe well is cooled by circulation or injection of a cold fluid.
 5. Themethod of claim 4, wherein the well is cooled via a workstring during adrilling/completion operation, or via the completion tubing or coiledtubing for an already completed well.
 6. The method of claim 4, whereinthe well is cooled with the group consisting of: water, sea water,completion brine, hydrocarbons as e.g. diesel, condensate or a drillingfluid, or by slurrying of dry ice in the injection stream or coolingthis stream at the surface with liquid nitrogen in a fluid/fluid heatexchanger.
 7. The method of claim 1, wherein a resin is used selectedfrom one or more of the following group consisting of: phenoliccondensation resins; epoxy resin compositions, in particular based ondiglycidyl ethers of bisphenols; ureum, phenol and melamine formaldehyderesins; latex compositions; room temperature vulcanizing silicone andfluorsilicone compounds and perfluoroether silicone hybrids.
 8. Themethod of claim 1, wherein the resin has a thermal expansion coefficientthat is greater than about 0.001 vol %/° C.
 9. The method of claim 1,wherein the resin is a vulcanizable rubber, selected from the followinggroup consisting of: natural rubbers, cis-polyisoprene rubber,nitrile-rubber, ethylene-propylene rubber, styrene butadiene rubber,butyl rubber, neoprene rubber, silicone rubbers, an room temperaturevulcanizing silicone rubber and/or a fluor-containing room temperaturevulcanizing silicone rubber.
 10. The method of claim 9, where a hybridof the rubbers plus conventional oil well cement (selected from ordinaryportland cement, blast furnace slag or aluminate) is used.
 11. Themethod of claim 1, wherein a cement pre-flush and/or after-flush isused.
 12. The method of claim 11, where in a plug and abandonmentoperation, the cement after-flush, if any, has a higher density than theresin, and/or wherein the cement after-flush, if any, has a lowerdensity than the resin.
 13. A method for removing a seal, plug orconnection made of an expanded resin according to claim 1, furthercomprising cooling the well wherein the seal, plug or connection is useduntil the seal, plug or connection has shrunk loose, and removing theloose seal, plug or connection.
 14. A method of analyzing the settingtime, elastic properties, shrinkage/expansion, compressibility orcoefficient of thermal expansion of thermosetting resins or oil wellcements under simulated reservoir pressure and temperature conditions,which comprises: introducing a sample of a thermosetting resin or oilwell cement into a pressure vessel that is equipped with a means toprovide the pressure and register the volume change and that canaccurately mimic realistic oil field conditions; at least partlyimmersing a body in the sample; filling the remaining volume of thevessel; exciting the body by an external outside force; and monitoringthe progress of the setting reaction on a continuous basis by afrequency/vibration) measurement, which encompasses the determination ofthe changing resonance frequency of the body that is at least partlyimmersed in the sample and which is excited by the external outsideforce.
 15. The method of claim 14, wherein the sample is introduced intoa non magnetic high pressure, high temperature pressure vessel, that isequipped with a pump capable of maintaining constant pressure by movinga piston; the body that is at least partly immersed is a flat spring;and wherein the external outside force that is used to excite the bodyis an external magnetic field.
 16. An analyzer for analyzing the settingtime, elastic properties, shrinkage/expansion, compressibility orcoefficient of thermal expansion of thermosetting resins or oil wellcements under simulated reservoir pressure and temperature conditions bythe method as claimed in claim 14.